`fib(35)` is a function to calculate 35th Fibonacci number.
```golang
fib := func(x) {
if x == 0 {
return 0
} else if x == 1 {
return 1
} else {
return fib(x-1) + fib(x-2)
}
}
fib(35)
```
`fibt(35)` is a [tail-call](https://en.wikipedia.org/wiki/Tail_call) version of `fib(35)`.
```golang
fibt := func(x, a, b) {
if x == 0 {
return a
} else if x == 1 {
return b
} else {
return fibt(x-1, b, a+b)
}
}
fibt(35, 0, 1)
```
Please see [tengobench](https://github.com/d5/tengobench) for more details.
## Tengo Syntax in 5 Minutes
Tengo supports line comments (`//...`) and block comments (`/* ... */`).
```golang
/*
multi-line block comments
*/
a := 5 // line comments
```
Tengo is a dynamically typed language, and, you can initialize the variables using `:=` operator.
```golang
a := 1984 // int
b := "aomame" // string
c := -9.22 // float
d := true // bool
e := '九' // char
f := [1, false, "foo"] // array
g := { // map
h: 439,
i: 12.34,
j: [0, 9, false]
}
k := func(l, m) { // function
return l + m
}
```
After the variable is initialized, it can be re-assigned different value using `=` operator.
```golang
a := 1928 // int
a = "foo" // string
f := func() {
a := false // 'a' is defined in the function scope
a = [1, 2, 3] // and thus does not affect 'a' in global scope.
}
print(a) // still "foo"
```
Type is not explicitly specified, but, you can use type coercion functions to convert between types.
```golang
s1 := string(1984) // "1984"
i2 := int("-999") // -999
f3 := float(-51) // -51.0
b4 := bool(1) // true
c5 := char("X") // 'X'
```
You can use dot selector (`.`) and indexer (`[]`) operator to read or write elemens of arrays or maps.
```golang
["one", "two", "three"][1] // == "two"
m := {
a: 1,
b: [2, 3, 4],
c: func() { return 10 }
}
m.a // == 1
m["b"][1] // == 3
m.c() // == 10
m.x = 5 // add 'x' to map 'm'
m.b[5] = 0 // but this is an error: index out of bounds
```
For sequence types (string or array), you can use slice operator (`[:]`) too.
```golang
[1, 2, 3, 4, 5][1:3] // == [2, 3]
[1, 2, 3, 4, 5][3:] // == [4, 5]
[1, 2, 3, 4, 5][:3] // == [1, 2, 3]
"hello world"[2:10] // == "llo worl"
```
In Tengo, functions are first-class citizen and be treated like any other variables. Tengo also supports closures, functions that captures variables in outer scopes. In the following example, the function that's being returned from `adder` function is capturing `base` variable.
```golang
adder := func(base) {
return func(x) { return base + x } // capturing 'base'
}
add5 := adder(5)
nine := add5(4) // nine
```
For flow control, Tengo currently supports **if-else**, **for**, **for-in** statements.
```golang
// IF-ELSE
if a <0{
// ...
} else if a == 0 {
// ...
} else {
// ...
}
// IF with init statement
if a := 0; a <10{
// ...
} else {
// ...
}
// FOR
for a:=0; a<10;a++{
// ...
}
// FOR condition-only (like WHILE in other languages)
for a <10{
// ...
}
// FOR-IN
for x in [1, 2, 3] { // array: element
// ...
}
for i, x in [1, 2, 3] { // array: index and element
// ...
}
for k, v in {k1: 1, k2: 2} { // map: key and value
To execute Tengo code in your Go codebase, you should use **Script**. In the simple use cases, all you need is to do is to create a new Script instance and call its `Script.Run()` function like this:
If you want to compile the source script and execute it multiple times, consider using `Script.Compile()` function that returns `Compiled` instance.
```golang
import (
"fmt"
"github.com/d5/tengo/script"
)
func main() {
s := script.New([]byte(`a := b + 20`))
// define variable 'b'
_ = s.Add("b", 10)
// compile the source
c, err := s.Compile()
if err != nil {
panic(err)
}
// run the compiled bytecode
// a compiled bytecode can be executed multiple without re-compiling it
if err := c.Run(); err != nil {
panic(err)
}
// retrieve value of 'a'
a := c.Get("a")
fmt.Println(a.Int())
}
```
In the example above, a variable `b` is defined by the user using `Script.Add()` function. Then a compiled bytecode (created by `Script.Compile()`) is used to execute the code and get the value of global variables, like `a` in this example.
If you want to use your own data type (outside Tengo's primitive types), you can create your `struct` that implements `objects.Object` interface _(and `objects.Callable` if you want to make function-like invokable objects)_.
```golang
import (
"errors"
"fmt"
"github.com/d5/tengo/compiler/token"
"github.com/d5/tengo/objects"
"github.com/d5/tengo/script"
)
type Counter struct {
value int64
}
func (o *Counter) TypeName() string {
return "counter"
}
func (o *Counter) String() string {
return fmt.Sprintf("Counter(%d)", o.value)
}
func (o *Counter) BinaryOp(op token.Token, rhs objects.Object) (objects.Object, error) {
switch rhs := rhs.(type) {
case *Counter:
switch op {
case token.Add:
return &Counter{value: o.value + rhs.value}, nil
case token.Sub:
return &Counter{value: o.value - rhs.value}, nil
}
case *objects.Int:
switch op {
case token.Add:
return &Counter{value: o.value + rhs.Value}, nil
case token.Sub:
return &Counter{value: o.value - rhs.Value}, nil
}
}
return nil, errors.New("invalid operator")
}
func (o *Counter) IsFalsy() bool {
return o.value == 0
}
func (o *Counter) Equals(t objects.Object) bool {
if tc, ok := t.(*Counter); ok {
return o.value == tc.value
}
return false
}
func (o *Counter) Copy() objects.Object {
return &Counter{value: o.value}
}
func (o *Counter) Call(args ...objects.Object) (objects.Object, error) {
Alternatively, you can directly create and interact with the parser, compiler and VMs directly. There's no good documentations for them, but, you can look at Script code to see how they work each other.
Although Tengo is designed as an embedded script language for Go, it can be compiled and executed as native binary without any Go code using `tengo` tool.
### Installing Tengo Tool
To install `tengo` tool, run:
```bash
go get github.com/d5/tengo/cmd/tengo
```
### Compiling and Executing Tengo Code
You can directly execute the Tengo source code by running `tengo` tool with your Tengo source file (`*.tengo`).
```bash
tengo myapp.tengo
```
Or, you can compile the code into a binary file and execute it later.